1. Field of the Invention
This invention pertains generally to implantable medical devices, and more particularly, to implantable drug delivery systems.
2. State of the Prior Art
Various types of implantable drug delivery systems are well-known in the prior art. Most such systems employ a reservoir or storage bladder for containing the drug in fluid form, a delivery catheter leading from the storage bladder to a blood vessel, and means for controlling the flow of the drug into the blood vessel. Some systems rely on simple difusion of the drug into the blood vessel, however, most systems employ a pumping means to force the drug into the vessel.
Common to all systems is the need to fill the storage bladder at regular intervals. In order to provide for release of the drug over an extended period of time, these devices are often filled with a drug in concentrated solution. The high concentration of the drug, in some cases, can lead to crystalization and accumulation of the drug within the delivery catheter, the storage bladder, or the internal passageways of the drug delivery system. These accumulations may interfere with the flow of the drug through the delivery catheter and may interfere with accurate dosage determination if crystallization and accumulation occurs within the storage bladder.